Polybutylene terephthalte resins are used as engineering plastics in wide fields including automobile parts, electric and electronic parts, or the like owing to their excellent mechanical properties, electric properties, and other physical and chemical properties, and their good workability. In particular, since their heat resistance and strength can be increased by adding a fibrous filler such as glass fiber thereto, polybutylene terephthalte resins are often used by reinforcing thereof by the fibrous filler.
Specifically in the automobile field, polybutylene terephthalate is often used as the material of sensor for electric control and of ECU housing. In that case, for the parts (insert molded articles) being mounted in an environment of severe temperature increase/decrease, such as engine room of automobile, the toughness of the parts is often improved by adopting an elastomer and the like to prevent crack generation caused by strain resulting from the difference in linear expansion between metal and resin. Many kinds of compositions have been proposed for that purpose.
For example, JP-A 3-285945 discloses the improvement in the resistance to heat shock by adding an elastomer such as ethylene-alkyl acrylate to polybutylene terephthalate. The resin, however, does not exhibit satisfactory resistance to heat shock and does not exhibit satisfactory resistance to hot water, although the improvement effect of those resistances is recognized in comparison with that of non-additive resin.
JP-A 60-210659 discloses the improvement of the resistance to hot water by adding an elastomer such as ethylene-alkyl acrylate and carbodiimide to polybutylene terephthalate. That kind of composition, however, does not exhibit satisfactory resistance to heat shock, although the resistance to hot water is improved.
Furthermore, JP-A 2001-234046 discloses that a resin composition composed of polybutylene terephthalate, a material providing impact resistance, and an aromatic polyvalent carboxylic acid ester compound exhibits excellent resistance to heat shock. However, the addition of the aromatic polyvalent carboxylic acid ester compound raises a problem of deteriorating the strength and the toughness, and also raises a problem of inducing bleeding at high temperatures.
As described above, although the addition of elastomer in order to improve the toughness is known, the addition thereof at an amount necessary for improving the toughness raises a problem of deteriorating the strength.